The effects of a stressed inshore urban reef on coral recruitment in Suva Harbour, Fiji

Abstract

A relic inshore reef ecosystem adjacent to the Fijian capital of Suva and another remote inshore reef were monitored monthly from July 2014 to July 2015 for coral recruitment, sedimentation rates, coral cover, temperature, and light intensity. Despite a major sewage spill in Suva Harbour in December 2014, the municipal inshore site exposed to constant anthropogenic activity, recorded no significant differences in coral spat abundance (except for the family Poritidae) on artificial substrata compared to the remote inshore site. Total yearly spat abundance was 106 on municipal reef and 132 on remote reef, while average daily sediment trap collection rates (g cm2/day) were significantly higher in the municipal site for the entire duration of monitoring. Total annual particulate organic matter content in sediment was also significantly higher in the municipal site (107.51 g cm2), compared to the remote site (43.37 g cm2). Mean light intensity was significantly lower for the municipal site (69.81 lum/ft2) compared to the remote site (239.26 lum/ft2), with Photosynthetically Active Radiation also lower for the former (800–1,066.66 µmol m−2 s−1) compared to the latter (3,266.66–3,600 µmol m−2 s−1). The lack of significant differences in coral spat recruitment rates suggests that settling larvae may be unable to distinguish between sub‐optimal and optimal sites probably as a consequence of interference with coral settlement cues arising from anthropogenic development.